270 DETECTION OP ARSENIC BY MEANS OP COPPER. 
This afforded a solution, which gave by Marsh's process an 
arsenical ring in a glass tube, and spots of the same nature 
on porcelain ; pure materials being used in the process. 
On the other hand, the second part of the urine was treated 
as proposed by M. Reinsch. The liquid was placed in a 
porcelain capsule, and reduced by evaporation to one-third ; 
on repose, a considerable deposit was formed. To this liquid 
200 grammes of pure hydrochloric acid was added ; the de- 
posit was immediately dissolved, and the liquid became of 
a deep brownish red color. Heating the liquid to ebullition, 
two plates of copper, perfectly clean, were placed in it, and 
retained for ten minutes. This being without effect, boiling 
was continued for half an hour, but with a similar result. 
The plates withdrawn from solution, washed and dried as 
directed by M. Reinsch, were not covered with a coating 
of an iron gray color ; they were brownish, from a coat- 
ing of brown oxide. One of the plates introduced into a 
glass tube, and heated, did not yield the least trace of arse- 
nious acid. 
These experiments appear to demonstrate, in opposition 
to the assertions of M. Reinsch, that this method does not 
rival in delicacy that of incineration by nitrate of potassa, 
or probably that of carbonization by sulphuric acid, although 
loss is sustained in both these latter operations. 
M. Reinsch asserts, that the method by copper, will detect 
the millionth of 0.050, equal to the 20,000th of 0.001 of arse- 
nious acid. Many experiments made, in which different 
quantities of arsenious acid had been added to urine, soup, 
water, &c. enabled me to perceive very distinctly, on the 
copper, the iron gray color, and to obtain afterwards, in a 
tube, appreciable quantities of arsenious acid, but only when 
about six-twentieths of 0.001 of the acid was added to the 
liquid ; or the great diversity of six-twentieths, instead of 
the twenty thousandth of a millegramme. 
I may add, that the method of M. Reinsch, has the serious 
inconvenience of introducing a salt of copper into the 
